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SU H6 - What needles are you running?

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Anthony_S

Anthony_S

Senior Member
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So I'm curious what everyone else out there is running for needles in their SU H6's? What vehicle are you running them in? I am running RH in my 1960 TR3A. I recently refurbished my carbs and put SM needles in and had problems getting the engine to idle at a lower rpm. After a lot of monkeying around I put the RH needles back in and was able to get it back down but it still idles pretty high, about 1500 rpms. So I have been doing a lot more reading and looking and I figure I have gone out of order and the timing is probably off, haven't checked that :p the valve clearances may be off too, so i need to check that. I also ordered a carb sync tool set so hopefully this will help when I get back to the carbs. I also put new butterflies in the carbs and I'm wondering if that might be causing a problem too. Maybe I didn't get them in there straight or something. But I now understand all this business with the carbs is futile until I get the other stuff straightened out :p I guess I'm just sharing all this cause I don't have anyone else to share it with. Sometimes I wish one of you guys where near by to stop by and help a friend out. But anyway I'm still curious what others are running for needles and any other thoughts or comments are welcome.

Thanks
Anthony!
 
The needles should have relatively little effect at idle. The RH needles are only richer through the midrange, IIRC the idle station is actually one (small) step leaner than the same station on the SM needles.

I tried the RH for awhile on my 3A, the extra fuel did give somewhat better throttle response and mid-range power; but the fuel mileage was way off. Someday, I plan to get a good (wide-band) exhaust meter, but for the moment I'm running the SM needles in my TR3 and they work pretty good.

You are right that all those things will affect idle rpm, but none of them should affect it so much that you can't kill the engine with the throttle. It can't run without air, no matter where the timing and valves and mixture are set. If backing off the idle screws won't kill it, then something is preventing the throttle plates from closing as they should.

Did you turn the throttle plates the right way over? It's not obvious, but the edges are tapered where they meet the carb bore, and the plate needs to be installed so the taper matches the bore. Centering is also important. And, as I just learned recently, it is important that the throttle stop (which also carries the idle adjustment screw) be firmly against the carb body when the throttle is fully closed. When I replaced the shafts many years ago, I apparently didn't get the front stop in just the right place. It didn't cause trouble at first, but I recently traced my problems with high idle to that fact. Adding a shim between the stop and carb body (so the plate could be centered with the stop firmly against the body) made the throttle work a lot nicer than it has.

FWIW, a 1/4" drive, 1/2" flex socket makes the carb R&R a lot easier and faster. I got mine at Sears.

https://i258.photobucket.com/albums/hh260/TR3driver/TS13571L/DSCF0018.jpg

DSCF0018.jpg
 
Randall,

I will have to check the throttle plates again. I didn't realize there was a certain way they went in. I will have to check the throttle stop too and make sure that is where it should be. I don't Think mine is touching the carb body right now. I did notice that when I put the new throttle plates in. The stop with the screw sits a bit above the carb body with the plates closed. Im thinking I may have the plates in backward. I did not change the throttle shafts so the stops are still in the same place as they where with the old plates.

Thanks
Anthony!
 
I'm running RH needles in my TR3A, but my engine has been modified and needed the extra fuel as shown by the O2 sensor I installed in the header.

Here's an SU Manual that I found very useful in getting my SU's into shape.
 
A run on the dyno showed that my 4A with 87mm pistons and a 25/65 cam was running lean in the mid range with the standard TR needles. I used one of the reference tables available on the net to set up an Excel table to compare TR, TS, SM and SB needles. I needed about an extra 10% in the mid range.

The SB showed nearly 30% more fuel at mid needle (station 8), the TS only 4% and the SM gave the desired 10% richer between stations 5 and 10. These figures are purely mathematical and someone much smarter than me would have to tell us how that translates into actual mixture. The car runs well and the mileage is reasonable on the SM needles. Interestingly, the SMs are about 2% leaner than the TS needles at full open, but I guess they don't spend too much time there.
 
Here's a downloadable SU program that I use. They have a free version, as well as a more complete version that costs a few pounds. I've been using the free version. It's fine most most applications, and kinda fun to mess around with.
 
Paul Tegler has an excellent chart showing a huge variety of needles and the measurement through the whole range, (sorry, I can't find the link right now.) You can make graphs, though it takes a while, of any needles that interest you so you can compare profiles before you decide. being able to read plugs will be a starting point but it would help to do a dyno run with mixture analysis.

What I use may not suit your car as mine is pretty heavily modified, cam, bigger valves, head work, electric fuel pump etc., so no point in telling you.
 
I'm running RH needles in my TR3 but I have a mild street cam and exhaust header and this setup works well for me. The idle is around 1500 but I have learned to live with it. I think a higher idle is needed because of the cam.
 
Something I noticed yesterday.....I was sitting in the driver seat and the car was off and the RPM needle was not at 0, it was close to 500. So is it safe to say I may not be idling as fast as I think I am. Also is there a way to get it to 0?
 
Definitely a possibility. Those old tachs frequently read high even when they do return to zero.

To make it read zero when stopped, you'll have to disassemble the case and remove the mechanism. Then you can hold the aluminum cup in your fingers, while you gently twist the needle on it's shaft to the desired position.

But before you do that, you might want to compare the tach reading to some other source (eg electronic tach) at several different speeds. Then you'll both know what to expect, and can move the needle to make it as accurate as possible.

I did have pretty good luck recalibrating my speedometer (which is the same mechanism as the tach, just has some extra dials and such), but the process wasn't trivial. I made a small degaussing tool from my soldering gun, a bolt and some insulated wire; plus a magnetizing tool from a U-bolt, more wire, some big capacitors and my bench DC power supply. Using those, I was able to adjust the strength of the flying magnet until the reading was very close (within 2-3 mph) from 10 mph to 80 mph. It still read high above 80, though.

Here's some more info on the speedo: https://home.comcast.net/~rhodes/speedo.html

As I mentioned, the tach uses the same mechanism, it just doesn't have the odometer and trip meter mechanisms mounted to it.
 
karls59tr said:
matrix-5. Your "3" is set up similar to mine. What rpm does your car idle at?
Click to expand...

Right now it runs at about 1000-1100 rpm when warmed up. I think I could get it a little lower, but at the moment I don't feel the need to.
 
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